This application claims priority to EP 01202274.5 filed Jun. 13, 2001.
The present invention relates to lithographic projection methods, systems, and apparatus and to products of such methods, systems, and apparatus.
The term xe2x80x9cpatterning structurexe2x80x9d as here employed should be broadly interpreted as referring to any structure or field that may be used to endow an incoming radiation beam with a patterned cross-section, corresponding to a pattern that is to be created in a target portion of a substrate; the term xe2x80x9clight valvexe2x80x9d can also be used in this context. Generally, such a pattern will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit or other device (see below). Examples of such patterning structure include:
A mask. The concept of a mask is well known in lithography, and it includes mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. Placement of such a mask in the radiation beam causes selective transmission (in the case of a transmissive mask) or reflection (in the case of a reflective mask) of the radiation impinging on the mask, according to the pattern on the mask. In the case of a mask, the support structure will generally be a mask table, which ensures that the mask can be held at a desired position in the incoming radiation beam, and that it can be moved relative to the beam if so desired.
A programmable mirror array. One example of such a device is a matrix-addressable surface having a viscoelastic control layer and a reflective surface. The basic principle behind such an apparatus is that (for example) addressed areas of the reflective surface reflect incident light as diffracted light, whereas unaddressed areas reflect incident light as undiffracted light. Using an appropriate filter, the said undiffracted light can be filtered out of the reflected beam, leaving only the diffracted light behind; in this manner, the beam becomes patterned according to the addressing pattern of the matrix-addressable surface. An alternative embodiment of a programmable mirror array employs a matrix arrangement of very small (possibly microscopic) mirrors, each of which can be individually tilted about an axis by applying a suitable localized electric field, or by employing piezoelectric actuation means. For example, the mirrors may be matrix-addressable, such that addressed mirrors will reflect an incoming radiation beam in a different direction to unaddressed mirrors; in this manner, the reflected beam is patterned according to the addressing pattern of the matrix-addressable mirrors. The required matrix addressing can be performed using suitable electronic means. In both of the situations described hereabove, the patterning structure can comprise one or more programmable mirror arrays. More information on mirror arrays as here referred to can be gleaned, for example, from U.S. Pat. Nos. 5,296,891 and 5,523,193, and PCT patent applications WO 98/38597 and WO 98/33096. In the case of a programmable mirror array, the said support structure may be embodied as a frame or table, for example, which may be fixed or movable as required.
A programmable LCD array. An example of such a construction is given in U.S. Pat. No. 5,229,872. As above, the support structure in this case may be embodied as a frame or table, for example, which may be fixed or movable as required.
For purposes of simplicity, the rest of this text may, at certain locations, specifically direct itself to examples involving a mask and mask table; however, the general principles discussed in such instances should be seen in the broader context of the patterning structure as hereabove set forth.
Lithographic projection apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, the patterning structure may generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. comprising one or more dies) on a substrate (e.g. a wafer of silicon or other semiconductor material) that has been coated with a layer of radiation-sensitive material (resist). In general, a single wafer will contain a whole network of adjacent target portions that are successively irradiated via the projection system, one at a time. In current apparatus, employing patterning by a mask on a mask table, a distinction can be made between two different types of machine. In one type of lithographic projection apparatus, each target portion is irradiated by exposing the entire mask pattern onto the target portion at once; such an apparatus is commonly referred to as a wafer stepper. In an alternative apparatusxe2x80x94commonly referred to as a step-and-scan apparatusxe2x80x94each target portion is irradiated by progressively scanning the mask pattern under the projection beam in a given reference direction (the xe2x80x9cscanningxe2x80x9d direction) while synchronously scanning the substrate table parallel or anti-parallel to this direction; since, in general, the projection system will have a magnification factor M (generally  less than 1), the speed V at which the substrate table is scanned will be a factor M times that at which the mask table is scanned. More information with regard to lithographic devices as here described can be gleaned, for example, from U.S. Pat. No. 6,046,792.
In a manufacturing process using a lithographic projection apparatus, a pattern (e.g. in a mask) is imaged onto a substrate that is at least partially covered by a layer of radiation-sensitive material (resist). Prior to this imaging step, the substrate may undergo various procedures, such as priming, resist coating and a soft bake. After exposure, the substrate may be subjected to other procedures, such as a post-exposure bake (PEB), development, a hard bake and measurement/inspection of the imaged features. This array of procedures is used as a basis to pattern an individual layer of a device, e.g. an IC. Such a patterned layer may then undergo various processes such as etching, ion-implantation (doping), metallization, oxidation, chemo-mechanical polishing, etc., all intended to finish off an individual layer. If several layers are required, then the whole procedure, or a variant thereof, will have to be repeated for each new layer. Eventually, an array of devices will be present on the substrate (wafer). These devices are then separated from one another by a technique such as dicing or sawing, whence the individual devices can be mounted on a carrier, connected to pins, etc. Further information regarding such processes can be obtained, for example, from the book xe2x80x9cMicrochip Fabrication: A Practical Guide to Semiconductor Processingxe2x80x9d, Third Edition, by Peter van Zant, McGraw Hill Publishing Co., 1997, ISBN 0-07-067250-4.
For the sake of simplicity, the projection system may hereinafter be referred to as the xe2x80x9clensxe2x80x9d; however, this term should be broadly interpreted as encompassing various types of projection system, including refractive optics, reflective optics, and catadioptric systems, for example. The radiation system may also include components operating according to any of these design types for directing, shaping or controlling the projection beam of radiation, and such components may also be referred to below, collectively or singularly, as a xe2x80x9clensxe2x80x9d. Further, the lithographic apparatus may be of a type having two or more substrate tables (and/or two or more mask tables). In such xe2x80x9cmultiple stagexe2x80x9d devices the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposures. Dual stage lithographic apparatus are described, for example, in U.S. Pat. No. 5,969,441 and PCT patent application WO 98/40791.
An image sensing device, which may be mounted on the substrate table, is used to measure a mark pattern present in the patterning structure so as to determine a plane of best focus of the lens, to determine lens aberrations, and to align the substrate table with respect to the patterning structure. Presently, an image sensor comprises several separate sensors located behind detection structures that may take the form of gratings. Generally, one type of detection structure is present above a single sensor, and several detection structures and respective sensors are required to determine the pattern characteristics as described. The detection structures may generally be processed in a single plate behind which the separate sensors are located.
The use of separate sensors requires a rather large distance between neighboring sensors. This requirement makes an imaging device that includes several complementary sensors and detection structures rather large, which may cause a problem when a narrow illumination field is being used and which may also limit measurements at the edge of the image field. Further, the present structured plate above the sensors may be somewhat unflat due to a mechanical treatment to make the detection structures and to mount it above the separate sensors. This shortcoming may cause capturing problems, since not all detection structures may be in best focus simultaneously.
Especially when short-wavelength radiation (such as extreme ultraviolet (EUV) radiation in the range of 10 to 15 nm) is used, the illumination field will become narrower and the requirements for the flatness of the plane in which the detection structures are present will become more stringent. Shorter wavelength radiation also requires the plate in which the detection structures are present to be thinner and the line widths of the detection structures to be smaller. A very flat image sensing plate is also required for a level sensor that may be used to determine height and tilt of the substrate table.
As described herein, embodiments of the present invention may include an image-sensing device of which separate sensors and respective detection structures are located very close so as to present limited dimensions.
Embodiments of the present invention may also include an image-sensing device of which a front surface is very flat such that the various detection structures are arranged in one well-defined plane.
Embodiments of the present invention may further include an image-sensing device of which dimensions are very insensitive to temperature variations.
One embodiment of the invention is a lithographic projection apparatus that is configured and arranged to image a pattern onto a substrate that is at least partially covered by a layer of radiation-sensitive material. This apparatus includes a radiation system configured and arranged to provide a projection beam of radiation, a support structure configured and arranged to support a patterning structure that serves to produce a desired pattern in the projection beam, a substrate table configured and arranged to hold the substrate, and a projection system configured and arranged to project the patterned projection beam onto a target portion of the substrate.
The apparatus also includes an image sensing device configured and arranged to measure a pattern in the patterned projection beam. The image sensing device includes a slab and a radiation-sensitive sensor arranged on a first side of the slab. The sensor is an integral part of said slab and is sensitive to the radiation of the projection beam.
The image sensing device also includes a film of a material that is non-transparent to the radiation of the projection beam. This film is provided on the first side of the slab over the sensor and includes one or more patterned segments above the sensor to selectively pass radiation of the projection beam to the sensor.
The apparatus also includes an intermediate plate made from a material having a thermal expansion coefficient below approximately 12xc3x9710xe2x88x926Kxe2x88x921. The slab is mounted such that a surface opposite to its first side faces a slab-bearing surface of the intermediate plate.
For at least some applications of such an apparatus, one or more sensors may be made accurately in a slab of material, preferably a wafer of semiconductor material, such as a silicon wafer, using semiconductor manufacturing techniques, and the slab preferably being polished to have very flat surfaces. Mechanical stability and a very good overall flatness is then achieved by mounting the slab onto the intermediate plate, which is also preferably polished to have a very flat slab-bearing surface. Direct bonding of slab to an intermediate proves to be a very strong and efficient means of attachment. Electrical connections to the sensors may now advantageously be provided through slab and intermediate plate to further electronics.
Another embodiment of the invention is a lithographic projection apparatus that is configured and arranged to image a pattern onto a substrate that is at least partially covered by a layer of radiation-sensitive material. This apparatus includes a radiation system configured and arranged to provide a projection beam of radiation, a support structure configured and arranged to support a patterning structure that serves to produce a desired pattern in the projection beam, a substrate table configured and arranged to hold the substrate, and a projection system configured and arranged to project the patterned projection beam onto a target portion of the substrate.
The apparatus also includes an image sensing device configured and arranged to measure a pattern in the patterned projection beam. The image sensing device includes a slab and at least two radiation-sensitive sensors arranged on a first side of the slab. The sensors are an integral part of said slab and are sensitive to the radiation of the projection beam.
The image sensing device also includes a film of a material that is non-transparent to the radiation of the projection beam. This film is provided on the first side of the slab over the sensors and includes one or more patterned segments above the sensors to selectively pass radiation of the projection beam to the sensors.
In this apparatus, at least one of the sensors is configured and arranged to measure an intensity of an unpatterned area in a cross-section of the patterned projection beam, and at least another one of said sensors is configured and arranged to measure an intensity of a patterned area neighboring the unpatterned area in the cross-section of the patterned projection beam. Each of the patterned segments above the sensors comprises a plurality of transmissive structures, a width of the transmissive structures within each patterned segment being at least substantially equal.
Another embodiment of the invention is a device manufacturing method that includes using a radiation system to provide a projection beam of radiation; using patterning structure to endow the projection beam with a pattern in its cross-section; and projecting the patterned beam of radiation onto a target portion of a layer of radiation-sensitive material that at least partially covers a substrate. This method also includes measuring a pattern in the patterned projection beam using an image sensing device that includes a slab; a radiation-sensitive sensor arranged on a first side of the slab, the sensor being an integral part of said slab and being sensitive to the radiation of the projection beam; and a film of a material that is non-transparent to the radiation of the projection beam. The film is provided on the first side of the slab over the sensor and has a patterned segment above the sensor configured and arranged to selectively pass radiation of the projection beam to the sensor. The slab is mounted with a surface opposite to the first side facing a slab-bearing surface of an intermediate plate made from a material having a thermal expansion coefficient below approximately 12xc3x9710xe2x88x926Kxe2x88x921.
Although specific reference may be made to this text to the use of the apparatus according to the invention in the manufacture of ICs, it should be explicitly understood that such an apparatus has many other possible applications. For example, it may be employed in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid-crystal display panels, thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms xe2x80x9creticlexe2x80x9d, xe2x80x9cwaferxe2x80x9d or xe2x80x9cdiexe2x80x9d in this text should be considered as being replaced by the more general terms xe2x80x9cmaskxe2x80x9d, xe2x80x9csubstratexe2x80x9d and xe2x80x9ctarget portionxe2x80x9d, respectively.
In the present document, the terms xe2x80x9cradiationxe2x80x9d and xe2x80x9cbeamxe2x80x9d are used to encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g. with a wavelength of 365, 248, 193, 157 or 126 nm) and extreme ultra-violet (EUV) radiation (e.g. having a wavelength in the range 5-20 nm), as well as particle beams, such as ion beams or electron beams.